Backside metal removal die singulation systems and related methods

ABSTRACT

Implementations of methods of singulating a plurality of die included in a substrate may include forming a groove through a backside metal layer through laser ablating a backside metal layer at a die street of a substrate and singulating a plurality of die included in the substrate through removing substrate material of the substrate in the die street.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application 62/796,630, entitled “BACKSIDE METALREMOVAL DIE SINGULATION SYSTEMS AND RELATED METHODS” to Michael J.Seddon, which was filed on Jan. 25, 2019, the disclosure of which ishereby incorporated entirely herein by reference.

BACKGROUND 1. Technical Field

Aspects of this document relate generally to plasma die singulationsystems and methods. More specific implementations involve methods ofsingulating semiconductor die from a substrate.

2. Background

Semiconductor devices include integrated circuits found in commonelectrical and electronic devices, such as phones, desktops, tablets,other computing devices, and other electronic devices. The devices areseparated through singulating a wafer of semiconducting material into aplurality of semiconductor die. Various layers may be coupled to thefront side and/or the backside of the wafer. Upon singulation, the diecan be mounted on a package and electrically integrated with the packagewhich may then be used in the electrical or electronic device.

SUMMARY

Implementations of methods of singulating a plurality of die included ina substrate may include forming a groove through a backside metal layerthrough laser ablating a backside metal layer at a die street of asubstrate and singulating a plurality of die included in the substratethrough removing substrate material of the substrate in the die street.

Implementations of methods of singulating a plurality of die included ina substrate may include one, all, or any of the following:

The substrate may be less than 50 micrometers thick.

The substrate may be less than 30 micrometers thick.

Removing the substrate material of the substrate in the die street mayinclude removing through one of sawing or lasering.

Removing the substrate material of the substrate in the die street mayinclude removing using plasma etching.

When removing the substrate material of the substrate in the die streetthrough sawing or lasering, the method may include removing damage froma sidewall of the die street through remote plasma healing.

Singulating the plurality of die comprised in the substrate throughplasma etching may include removing a portion of the substrate materialof the substrate having a width less than a width of the die street.

Implementations of methods of singulating a plurality of die included ina substrate may include forming, on a first side of a substrate, one ormore layers, forming a backside metal layer on the second side of thesubstrate, laser ablating a groove into the backside metal layer toexpose at least a portion of the substrate, and singulating a pluralityof die comprised in the substrate through plasma etching at the portionof the substrate exposed by the groove. The groove may be located in adie street of the substrate.

Implementations of methods of singulating a plurality of die included ina substrate may include one, all, or any of the following:

Singulating a plurality of die included in the substrate through plasmaetching may include plasma etching from the second side of thesubstrate,

The method may include thinning the second side of the substrate to lessthan 50 micrometers thick.

The method of singulating a plurality of die in a substrate may includemonitoring the laser ablation of the groove using a camera facing thesecond side of the substrate.

The method of singulating a plurality of die in a substrate may includemaking near-real-time adjustments to one or more laser parameters basedupon data collected through monitoring the laser ablation of the grooveusing a camera facing the second side of the substrate.

Singulating the plurality of die comprised in the substrate throughplasma etching may include removing a portion of the substrate materialof the substrate having a width less than a width of the die street.

The backside metal layer may include copper.

Implementations of methods of singulating a plurality of die included ina substrate may include using a laser, grooving through a backside metallayer in a die street coupled to a substrate, actively monitoring aformation of a groove in the backside metal layer, and singulating aplurality of die included in the substrate through removing a substratematerial at the grooves in the back metal layer.

Implementations of methods of singulating a plurality of die included ina substrate may include one, all, or any of the following:

Actively monitoring the formation of the groove in the backside metallayer may include monitoring using a camera facing the backside metallayer.

The method of singulating a plurality of die in a substrate may includemaking near-real-time adjustments to one or more laser parameters basedupon data collected through monitoring the formation of the groove usinga camera facing the second side of the substrate.

Removing the substrate material at the grooves may include removingthrough plasma etching.

The method of singulating a plurality of die from a substrate mayinclude removing damage from a sidewall of the die street through remoteplasma healing.

The substrate may be thinned to less than 50 micrometers.

The foregoing and other aspects, features, and advantages will beapparent to those artisans of ordinary skill in the art from theDESCRIPTION and DRAWINGS, and from the CLAIMS.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations will hereinafter be described in conjunction with theappended drawings, where like designations denote like elements, and:

FIG. 1 is a cross sectional side view of a portion of a substrate;

FIG. 2 is a cross sectional side view of a plurality of layers coupledto a first side of the substrate of FIG. 1;

FIG. 3 is a view of the substrate and plurality of layers of FIG. 2 in aflipped orientation;

FIG. 4 is a view of substrate and plurality of layers of FIG. 3 with thesubstrate thinned;

FIG. 5 is a view of thinned substrate and plurality of layers of FIG. 4with a backside metal layer coupled to the second side of the substrate;

FIG. 6 is a view of the backside metal layer of FIG. 5 having a grooveformed therein;

FIG. 7 is a view of the substrate of FIG. 6 singulated into a pluralityof die;

FIG. 8 is a view of a backside metal layer coupled to a substrate;

FIG. 9 is a view of the backside metal layer of FIG. 8 having a grooveformed therein;

FIG. 10 is a view of the substrate of FIG. 9 singulated into a pluralityof die; and

FIG. 11 is a view of the plurality of die of FIG. 10 havingsmoothed/healed sidewalls.

DESCRIPTION

This disclosure, its aspects and implementations, are not limited to thespecific components, assembly procedures or method elements disclosedherein. Many additional components, assembly procedures and/or methodelements known in the art consistent with the intended backside metalremoval die singulation systems and related methods will become apparentfor use with particular implementations from this disclosure.Accordingly, for example, although particular implementations aredisclosed, such implementations and implementing components may compriseany shape, size, style, type, model, version, measurement,concentration, material, quantity, method element, step, and/or the likeas is known in the art for such backside metal removal die singulationsystems and related methods, and implementing components and methods,consistent with the intended operation and methods.

Referring to FIG. 1, a cross sectional side view of a portion of asubstrate 2 is illustrated. The term “substrate” refers to asemiconductor substrate as a semiconductor substrate is a common type ofsubstrate, however, “substrate” is not an exclusive term that is used torefer to all semiconductor substrate types. Similarly, the term“substrate,” may refer to a wafer as a wafer is a common type ofsubstrate, however, “substrate” is not an exclusive term that is used torefer to all wafers. The various semiconductor substrate types disclosedin this document that may be utilized in various implementations may be,by non-limiting example, round, rounded, square, rectangular, or anyother closed shape. In various implementations, the substrate 2 mayinclude various substrate materials such as, by non-limiting example,single crystal silicon, silicon dioxide, glass, gallium arsenide,sapphire, ruby, silicon-on-insulator, silicon carbide, polycrystallineor amorphous forms of any of the foregoing, and any other substratematerial useful for constructing semiconductor devices. In particularimplementations, the substrate may be a silicon-on-insulator substrate.

Referring to FIG. 2, a cross sectional side view of a plurality oflayers 4 coupled to a first side of the substrate of FIG. 1 isillustrated. In various implementations, before singulating a pluralityof die from the substrate 2, the method of forming a plurality of diemay include forming a plurality of die on the substrate. This mayinclude forming a plurality of layers 4 on a first side 6 the substrate2. As illustrated by FIG. 2, the plurality of layers 4 may be patterned,and in various implementations, may be patterned (or otherwise removed)to not be present in a die street 8 area of the substrate 2. Theplurality of layers may include, by non-limiting example, one or moremetal layers, one or more passivation layers, any other layer, and anycombination thereof. In various implementations passivation layers mayinclude, by non-limiting example, silicon nitride, oxides, metalelectrical test structures, electrical test pads, silicon dioxide,polyimides, metal pads, residual underbump metallization (UBM), anycombination thereof, and any other layer or material capable offacilitating electrical or thermal connection between the one or moresemiconductor die and/or protecting the one or more semiconductor diefrom contaminants. In various implementations, the plurality of die mayinclude power semiconductor devices, such as, by non-limiting example, aMOSFET, an IGBT, or any other power semiconductor device. In otherimplementations, the plurality of die may include non-powersemiconductor devices.

Referring to FIG. 3, a view of the substrate and plurality of layers ofFIG. 2 in a flipped orientation is illustrated. The method of formingand singulating a plurality of die includes flipping the substrate and,though not illustrated, in various implementations, the method mayinclude applying a tape to a first side 10 of the plurality of layers 4.Such a tape may be a backgrinding tape in various implementations.Referring to FIG. 4, a view of substrate and plurality of layers of FIG.3 with the substrate thinned is illustrated. In various implementations,the method of forming and singulating a plurality of die may includethinning the second side 12 of the substrate 2. In variousimplementations, the substrate 2 may be thinned to a thickness less than50 micrometers (μm). In other implementations, the substrate 2 may bethinned to a thickness less than 30 μm. In still other implementations,the substrate 2 may be thinned to a thickness less than 100 μm, morethan 100 μm, and in other various implementations, the substrate 2 maynot be thinned. In particular implementations, the substrate 2 may bethinned to a thickness of about 25 μm, and in other particularimplementations, the substrate may be thinned to a thickness of about 75μm. The substrate 2 may be thinned through backgrinding, etching, or anyother thinning technique. In particular implementations, the substrateis thinned using a backgrinding process marketed under the trade nameTAIKO by DISCO of Tokyo, Japan to provide an edge ring supporting thethinned substrate.

Referring to FIG. 5, a view of the thinned substrate and plurality oflayers of FIG. 4 with a backside metal layer coupled to the second sideof the substrate is illustrated. The method of forming a plurality ofdie and singulating the plurality of die includes forming a backsidemetal layer 14 on the second side of the substrate 2. In particularimplementations, the backside metal layer 14 may be copper or a copperalloy. In other implementations, the backside metal layer may includeany other type of metal, alloy thereof, or combination thereof. Invarious implementations, the backside metal layer may include anadhesion layer like Ti, TiW, TiN, and/or Al, and any combination thereoffollowed by a layer of a diffusion barrier such as Ni, NiV, and/or Cu,and any combination thereof followed by an oxide inhibitor (to protectthe diffusion barrier from oxidizing) and a solderable metal such as Au,Ag, and/or Sn and any combination thereof. In various implementations,the backside metal layer may be 10 μm thick. In other implementations,the backside metal layer may be more or less thick than 10 μm. Inimplementations where 10 μm of Cu is used, then a seed metal layer orunder bump metal layer (UBM) may be deposited which is used used forelectrolytic plating. The seed metal layers typically comprise of anadhesion layer like that previously discussed (Al, Ti, TiW, and/or TiN,or any combination thereof) followed the plated material (Cu or Ni),followed by a diffusion barrier for the diffusion layer such as Au, Sn,and/or Ag or any combination there. The backside metal layer 14 may beevaporated or sputtered onto the substrate 2, however, in otherimplementations (including implementations having thicker substrates),the backside metal layer 14 may be plated onto the substrate 2 or formedon the substrate using another technique. In various implementations,the backside metal layer 14 may be formed over the entire second side 12of the substrate 2. In such implementations, the backside metal layer 14may strengthen the substrate 2. In various implementations, the outersurface 16 of the backside metal layer may be coated with a film orother layer in order to facilitate removal of any slag resulting fromthe laser ablation disclosed later herein. This layer may be appliedusing spray coating, spin coating, or other coating techniques.

Prior to any actual singulation of a plurality of the die, the method ofsingulating the plurality of die in the substrate may include aligningthe substrate. In various implementations, the method may includealigning the substrate from the first side (which may be the front side,or bottom/tape facing side as oriented in FIG. 5) using optics or acamera. In such implementations, the optics or camera may be placedbelow the substrate and may detect a plurality of alignment featuresformed on or within the substrate. In various implementations, thealignment features may be formed on or within the die street 8 of thesubstrate. In implementations having tape coupled to the first side 10of the plurality of layers, the optics or camera may be configured todetect the plurality of alignment features through the tape. In aparticular implementation, the substrate may be aligned using aninfrared (IR) camera and IR alignment features. In otherimplementations, the alignment features may be included on an outersurface 16 of the backside metal layer 14. In such implementations,rather than requiring optics or a camera to be below the substrate, theoptics or camera may align the substrate from above the substrate (asoriented in FIG. 5). In still other implementations where the substrateincludes a ring around the perimeter after thinning the substrate, themethod of aligning the substrate may include placing alignment featuresin the periphery of the substrate and grinding down the perimeter ring.The substrate may then be aligned from the backside, or second side 12of the substrate by using the alignment features along the outer edge ofthe device. Such an alignment method may include using an IR camera.

Referring to FIG. 6, a view of the backside metal layer of FIG. 5 havinga groove formed therein is illustrated. Upon aligning the substrate, themethod of singulating a plurality of die in the substrate 2 includesforming a groove 18 through the backside metal layer 14. The groove 18is located in/positioned in the die street 8. In variousimplementations, the groove 18 may be as wide as the die street 8 orwider than the die street. The groove 18 may be formed through laserablating a backside metal layer 14 at the die street 8 of the substrate2. As illustrated, in various implementations the groove 18 extendsthrough the backside metal layer 14. In this manner, at least a portion20 of the substrate 2 is exposed. In various implementations, theformation of the groove is stopped at the substrate 2. Because laserablation may form a groove more slowly in the backside metal layer 14 ascompared to the substrate 2, care may be required to prevent the laserbeam from laser ablating a groove deep into, or through, the substrate2. In order to facilitate the formation of the groove 18 stopping at thesubstrate 2, in various implementations the method includes activelymonitoring the formation of a groove 18 in the backside metal layer 14.In various implementations, a camera facing the backside metal layer 14may be used to actively monitor the formation of the groove 18. Activemonitoring may include monitoring the cleared backside metal and/ormeasuring the thickness variation of the removed backside metal layer ascompared to the original thickness of the backside metal layer.

In such implementations, near-real-time adjustments may be made to oneor more laser parameters based upon data collected during the activemonitoring to alter the laser characteristics to ensure just the backmetal is being ablated. In particular implementations, near-real-timeadjustments may include the camera monitoring the formation of thegroove one inch behind the laser beam, and, based upon the datacollected from the monitoring, immediately making adjustments to theparameters of the laser. In other implementations, near-real-timeadjustments may include the camera actively monitoring the formation ofthe groove less than one inch behind the laser beam or more than oneinch behind the laser beam. The parameters of the laser beam which maybe adjusted may include, by non-limiting example, laser power, pulseenergy, pulse frequency, spot size, focal point, focal depth, and/orspeed of movement of the laser beam across the backside metal layer 14.In various implementations, especially implementations involving thinnedsubstrates, active monitoring of the formation of the groove 18 may becritical as the process window for forming the groove may be narrow.This is in part because variations in the thickness of the tape uponwhich the thinned substrate is mounted may be 5 microns or more acrossthe tape, meaning that for a back metal layer of 10 microns thickness,the laser beam will see 50% variation in apparent thickness of the backmetal layer at a particular focal depth just because of tape thicknessvariation. Through such active monitoring and near-real-timeadjustments, any tilt in the substrate or chuck and any variations inthe thickness of the tape may be compensated for by adjusting theparameters of the laser. In this manner, the backside metal layer 14 mayhave a groove 18 formed entirely through the thickness without thegroove being formed into (or substantially into) the substrate 2.

Referring to FIG. 7, a view of the substrate of FIG. 6 singulated into aplurality of die is illustrated. The method of singulating a pluralityof die 22 in a substrate 2 includes singulating the plurality of die inthe substrate through removing substrate material of the substrate 2 atthe grooves 18 in the die street 8. As illustrated by FIG. 7, theplurality of die are singulated from the backside of the substrate.Because of this, there is no need to flip the substrate over in order tosingulate the substrate from the front side. The ability to singulatethe die from the backside may reduce damage to the substrate, andespecially a thinned substrate, as it requires the substrate to behandled less, increasing the yield of the process correspondingly.Further, in implementations where the plurality of die are singulatedfrom the backside through laser ablation (as disclosed later herein),because it is singulated from the backside and not the front side,redeposition of the back metal layer may be reduced as residualbackmetal may more easily flow away from the sidewalls of the die.

In various implementations, the plurality of die 22 may be singulatedthrough removing the substrate material of the substrate 2 in the diestreet 8 through plasma etching from the second side 6 of the substrate2 at the portion 20 of the substrate exposed by the groove 18. Invarious implementations, a plasma etch process marketed under thetradename BOSCH® by Robert Bosch GmbH, of Stuttgart, Germany (the “Boschprocess”), may be used to singulate the substrate 2 into a plurality ofdie 22. In other implementations, other plasma etch processes may beused to singulate the plurality of die 22 from the substrate 2. Invarious implementations, though not illustrated herein, singulating theplurality of die included in the substrate through plasma etching mayinclude removing a portion of the substrate material of the substratehaving a width less than a width of the die street. In suchimplementations, the width of the removed portion from plasma etching isless than the width of the die street as plasma die singulation iscapable (with the use of photolithography or other masking techniques)of creating a die street narrower than the die street created throughlaser ablation. In other implementations, and as illustrated by FIG. 7,the width of the removed portion of the substrate may be the same as thewidth of the die street 8 by singulating the plurality of die 22 throughremoving through plasma etch all of the substrate material of thesubstrate 2 in the die street 8.

Referring to FIGS. 8-11, a method for singulating a plurality of diesimilar to the method illustrated by FIGS. 5-7 is illustrated. Referringspecifically to FIG. 8, a view of a backside metal layer coupled to asubstrate is illustrated. The substrate 28 may be the same as or similarto any substrate disclosed herein, the plurality of layers 32 coupled tothe substrate may be the same as or similar to any type of plurality oflayers disclosed herein, and the backside metal layer 30 may include anytype of backside metal layer disclosed herein. Likewise, the backsidemetal layer 30, the plurality of layers 32, and the substrate 28 may beformed using the same or a similar method as any method disclosedherein. The method of singulating a plurality of die may also includealigning the substrate using any alignment technique disclosed herein.Referring to FIG. 9, a view of the backmetal layer of FIG. 8 having agroove formed therein is illustrated. The method of singulating aplurality of die includes forming a groove 34 in the backside metallayer 30 using the same or a similar method as the methods for forminggrooves disclosed herein. As illustrated by FIG. 9, the sidewalls 36 ofthe groove 34 may be rough as a result of the laser ablation.

Referring to FIG. 10, a view of the substrate of FIG. 9 singulated intoa plurality of die is illustrated. The method of singulating a pluralityof die 38 in a substrate 28 includes singulating the plurality of die inthe substrate through removing substrate material of the substrate 28 atthe grooves 34 in the die street 40. As illustrated by FIG. 10, theplurality of die are singulated from the second side 42, or backside, ofthe substrate 28. Because of this, there is no need to flip thesubstrate 28 over in order to singulate the substrate from the frontside. As previously discussed, the ability to singulate the plurality ofdie 38 from the backside of the substrate 28 may reduce damage to thesubstrate, and especially a thinned substrate, as it requires thesubstrate 28 to be handled less. In various implementations, theplurality of die 38 may be singulated through removing the substratematerial of the substrate 28 in the die street 40 through sawing orlasering at the exposed portion 42 of the substrate 28 exposed by thegroove 34. In particular implementations, the method of singulating theplurality of die may include forming the groove 34 through laserablation and singulating the plurality of die 38 through laser ablation.The two-step laser ablation process may prevent re-deposition of thebackside metal layer 30 into the substrate 28 as the backside metallayer 30 in the die street 40 will be cleared away prior to thesingulation of the plurality of die 38.

As illustrated by FIG. 10, when singulating the plurality of die 38using a laser beam or a saw blade, the sidewalls 44 of each die resultsin the production of damage, chips, and/or cracks in the sidewalls 44 ofthe die street 40 and layers adjacent to the die street. The presence ofthe cracks and chips has the potential to compromise the reliability ofthe resulting semiconductor package (and reduce the die strength)if/when the cracks and chips propagate into the device portion of thesemiconductor die. Since the saw process involves the rubbing of therotating blade against the substrate surface, and the laser processinvolves melting and ablating the material under the focus of a laserbeam on the substrate surface, the damage, chipping, and cracking canonly be influenced through saw or laser processing variables (such as,by non-limiting example, substrate feed speed, blade kerf width, cutdepth, multiple saw cuts, blade materials, laser power, focal depth,pulse energy, pulse repetition rate, etc.) but not eliminated entirely.

Referring to FIG. 11, a view of the plurality of die of FIG. 10 havingsmoothed sidewalls is illustrated. In implementations where theplurality of die 38 are singulated through lasering or sawing, themethod of singulating the plurality of die may include removing damagefrom a sidewall 44 of the die street 40 through remote plasma healing.In such implementations, an isotropic or substantially isotropic plasmaetch may be applied to the sidewalls 44 of the die street 40. The plasmamay penetrate/facilitate reaction with the materials of the cracksand/or chips of the sidewalls 44 formed when the plurality of die 38were singulated from the substrate 28. As the plasma encounters thecracks and/or chips, the damaged portion(s) of the substrate 28 may etchaway and result in smoothed, or healed, sidewalls 44 of the die street,as illustrated by FIG. 11.

In places where the description above refers to particularimplementations of backside metal removal die singulation systems andrelated methods and implementing components, sub-components, methods andsub-methods, it should be readily apparent that a number ofmodifications may be made without departing from the spirit thereof andthat these implementations, implementing components, sub-components,methods and sub-methods may be applied to other backside metal removaldie singulation systems and related methods.

What is claimed is:
 1. A method of singulating a plurality of diecomprised in a substrate, the method comprising: forming a groovethrough a backside metal layer through laser ablating the backside metallayer at a die street of a substrate; and singulating a plurality of diecomprised in the substrate through plasma etching at the die street;wherein singulating the plurality of die comprised in the substratethrough plasma etching further comprises removing a portion of thesubstrate having a width less than a width of the die street; andwherein the backside metal layer is used as a mask for the plasmaetching at the die street.
 2. The method of claim 1, wherein thesubstrate is less than 50 micrometers thick.
 3. The method of claim 1,wherein the substrate is less than 30 micrometers thick.
 4. A method ofsingulating a plurality of die comprised in a substrate, the methodcomprising: forming, on a first side of a substrate, one or more layers;forming a backside metal layer on a second side of the substrate; laserablating a groove into the backside metal layer to expose at least aportion of the substrate, wherein the groove is located in a die streetof the substrate; using the backside metal layer as a mask, singulatinga plurality of die comprised in the substrate through plasma etching,from the second side of the substrate, at the portion of the substrateexposed by the groove; monitoring the laser ablating of the groove; andmaking near-real-time adjustments to one or more laser parameters basedupon data collected through the monitoring.
 5. The method of claim 4,further comprising thinning the second side of the substrate, whereinthe substrate is thinned to less than 50 micrometers.
 6. The method ofclaim 4, further comprising monitoring the laser ablating of the grooveusing a camera facing the second side of the substrate.
 7. The method ofclaim 4, wherein singulating the plurality of die comprised in thesubstrate through plasma etching further comprises removing a portion ofthe substrate having a width less than a width of the die street.
 8. Themethod of claim 4, wherein the backside metal layer comprises copper. 9.A method of singulating a plurality of die comprised in a substrate, themethod comprising: using a laser, grooving through a backside metallayer in a die street coupled to a substrate; actively monitoring aformation of a groove in the backside metal layer; and using thebackside metal layer as a mask, singulating a plurality of die comprisedin the substrate through removing, from a side of the substrate facingthe backside metal layer, substrate material at the groove in thebackside metal layer.
 10. The method of claim 9, wherein activelymonitoring the formation of the groove in the backside metal layerfurther comprises monitoring using a camera facing the backside metallayer.
 11. The method of claim 10, further comprising makingnear-real-time adjustments to one or more laser parameters based upondata collected during the monitoring.
 12. The method of claim 9, whereinremoving the substrate material at the groove further comprises removingthrough plasma etching.
 13. The method of claim 9, further comprisingremoving damage from a sidewall of the die street through remote plasmahealing.
 14. The method of claim 9, wherein the substrate is thinned toless than 50 micrometers.
 15. The method of claim 4, wherein singulatingthe plurality of die comprised in the substrate through plasma etchingfurther comprises removing a portion of the substrate having a widthless than a width of the die street.
 16. The method of claim 9, whereinsingulating the plurality of die comprised in the substrate furthercomprises removing a portion of the substrate having a width less than awidth of the die street.